The invention relates to polymerization retarders and inhibitors in general and to stabilizing agents for prevention of premature polymerization of ar-brominated styrene monomer in particular.
Vinyl aromatic compounds tend to polymerize on standing. During the manufacture, shipping, and storage of these compounds, inhibitors are normally added to prevent or highly retard polymerization until such time that these compounds are intentionally converted to polymers.
Dozens of stabilizing agents for prevention of undesirable polymerization of monomers in general have been reported in the literature. As noted by Czechoslovakian Patent Document No. 163,428 (Konecny et al) compositions which are known to stabilize one or more monomers include: sulfur, copper, silver, gold, activated carbon, triphenylarsine, NH.sub.3, diazoaminobenzene, some diolefins, phenylacetylene, sym-trinitrobenzene, p-benzoquinone, acetaldehyde, aniline condensates, N,N'-dibutyl-o-phenylenediamine, N-butyl-p-aminophenol, 2,4,6-triphenylphenoxyl, pyrogallol, pyrocatechol, hydroquineone, alkyl-substituted pyroactechols, dialklhydroquinone, 2,4,6-di-chloronitrophenol, halogen-ortho-nitrophenols, alkoxyhydroquinone, mono-, di-, and polysulfides of phenols and pyrocatechols, aromatic nitrocompounds, amines, thiols, oximes or hydrazones of quinone, phenothiazine, dialkylhydroxylamines, and nitro compounds. However, as also noted by Konecny et al only a few of the known stabilizers are commercially employed with benzoquinone, hydroquinone, and tert-butylpyrocatechol mentioned by name. The other stabilizers have various shortcomings including undesirable levels of toxicity, explosiveness, or insufficient stabilizing activity. Also, many of the above listed compounds are noted to be stabilizers in conjunction with only a limited group of monomers. Konecny et al suggest use of a synergistic mixture of 2,4 dinitro-o-cresol and diethylhydroxylamine with styrene and divinyl benzene.
In 1960 a process for stabilizing vinyl aromatics such as styrene was described in U.S. Pat. No. 2,965,685 (Campbell) which utilized N,N-dialkylhydroxylamines such as N,N-diethylhydroxylamine (DEHA). Recommended levels of inhibitor are said to be from about 0.001% to about 5% by weight.
In 1966 aliphatic carboxylic acid salts of DEHA were described as stabilizers for aromatic vinyl compounds such as styrene in U.S. Pat. No. 3,248,440 (Albert).
While diethylhydroxylamine-containing compositions have been described as among a plethora of types of chemicals useful for stabilizing vinyl aromatic compounds such as styrene, its use with brominated styrenes has not been addressed. Only a few compositions have been described as useful for stabilizing ar-brominated styrenes such as dibromostyrene.
In British Patent Document No. 1,230,979, dibromostyrene (DBS) is described as being stabilized by picric acid or by a mixture of picric acid with a quinone or phenol such as hydroquinone, benzoquinone and t-butyl catechol. Unfortunately picric acid has the undesirable characteristics of coloring monomers bright yellow and, when concentrated, being shock sensitive.
Also, U.S. Pat. No. 4,276,189 (Jackisch) describes a process for retarding polmerization of dibromostyrene by addition of a metal oxide such as magnesium, calcium, or zinc oxide with or without an additional stabilizing agent such as 4-tert-butylcatechol and most benzoquinones.